Polyester resins stabilized with sulfones



United States Patent 3,546,164 POLYESTER RESINS STABILIZED WITH SULFONESMary J. Stewart, Riddlewood, Media, and Otto K. Carlson, Marcus Hook,Pa., assignors to FMC Corporation, Philadelphia, Pa., a corporation ofDelaware No Drawing. Filed Apr. 19, 1968, Ser. No. 722,542 Int. Cl. C08gUS. Cl. 260-4535 10 Claims ABSTRACT OF THE DISCLOSURE A thermalstabilized polyester comprising a highly polymeric linear polyester anda compound selected from those represented by the formula wherein R andR are radicals selected from the group consisting of alkyl containingfrom 1 to 10 carbon atoms, phenyl and chlorine, hydroxyl or lower alkylpara substituted phenyl.

This invention relates to highly polymeric linear polyester resins thatpossess improved thermal stability and to a method of producing same.

The fiber and film-forming linear polyester resins used in the presentinvention, which are known as saturated linear polyesters, can beprepared by first carrying out a condensation reaction between anaromatic dicarboxylic acid or ester thereof which does not contain anyethylenic unsaturation and a suitable diol to form a prepolymer. Theresulting prepolymer is then polycondensed to form the desired saturatedlinear polyester resin. When an ester of a dicarboxylic acid is used asthe starting material, it is first reacted with a diol in the presenceof a transesterification or ester-interchange catalyst by means of anester-interchange reaction; whereas when a dicarboxylic acid is used asthe starting material, it is first subjected to a direct esterificationreaction with a diol in the presence of What is generally called a firststage additive or ether inhibitor. In either instance, the resultingreaction product. which may be generally described as a polyesterprepolymer, is then polycondensed in the presence of a polycondensationcatalyst to form a polyester resin.

For example, in the case of the transesterification method of preparingpolyethylene terephthalate, ethylene glycol is reacted with dimethylterephthalate to form a polyester prepolymer which is comprised mainlyof bis- 2-hydroxyethyl terephthalate; or in the direct esterificationmethod, ethylene glycol is reacted with terephthalic acid to form theresulting polyester prepolymer which is then polycondensed to form thedesired polyester resin.

Linear polyester resins, such as polyethylene terephthalate and others,are widely used in the production of films and fibers and the like.However, it is generally known that such polyester products degrade whenexposed to heat for a substantial period of time. Such deg radation isparticularly a problem in the extrusion and spinning process of thefinished resins to form the abovedenoted products. Additionally, thefibers produced from such resins are extensively used in the textilefield and, as a result of this application, are subjected to ratherextreme temperatures in the processes of washing, drying, and ironing.Therefore, it is highly desirable that the polyester resin compositionpossess as much stability at high temperatures as possible.

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Therefore, it is an object of the present invention to prepare a highlypolymeric linear polyester resin composition which exhibits improvedthermal stability.

Another object of the present invention is to provide a method ofpreparing linear polyester resin exhibiting such a high degree ofthermal stability.

These and other subjects are accomplished in accordance with the presentinvention with a stabilized polyester composition comprising a highlypolymeric linear polyester containing a stabilizing amount of a compoundselected from those represented by the formula wherein R and R areradicals selected from the group consisting of alkyl containing from 1to 10 carbon atoms, phenyl and chlorine, hydroxyl or lower alkyl (C Cpara substituted phenyl. The term para substituted phenyl used above andhereinafter, denotes phenyl radicals substituted in the 4-position.

Among the sulfone compounds which can be used as thermal stabilizers inthe present invention are, for example, di-n-ethyl sulfone, di-n-hexylsulfone, di-n-butyl sulfone. di-n-octyl sulfone, di-n-decyl sulfone,di-p-hydroxyphenyl sulfone, di-p-chlorophenyl sulfone, di-p-tolylsulfone, di-p-pentylphenyl sulfone, di-p-ethyl-phenyl sulfone, andhexylphenyl sulfone.

The highly polymeric linear polyester resins used in the preparation ofthe subject thermal stabilized polyester compositions can be preparedvia either the conventional ester-interchange reaction or directesterification method, both of which are thoroughly disclosed throughoutthe prior art.

In the practice of the present invention, it has been found that it ispreferred to thoroughly mix or blend the present thermal stabilizers inthe polyester resin immediately after the polycondensation step has beencompleted, at atmospheric pressure, while the resin is still molten inorder to form a uniform blend of polyester resin and a thermalstabilizer of the present invention.

It has been found that the present thermal stabilizers, as definedabove, are effective as such in polyester resin compositions whenemployed in amounts ranging from about 0.01% to about 0.5%, by weight,based on the weight of the linear polyester resin. Usually, it has beenfound that concentrations ranging from about 0.02% to about 0.3%, byweight, are preferred in most instances. However, when indicated,concentrations less or greater than the above can be used, but theireffectiveness is generally reduced proportionally.

The following examples will further serve to illustrate the presentinvention, although it Will be understood that these examples areincluded merely for the purpose of illustration and are not intended tolimit the scope of the present invention. All parts are by weight,unless otherwise indicated.

EXAMPLE I A blended mixture comprising 474 g. of terephthalic acid, 288ml. of ethylene glycol and 149 ml. of triethylamine was charged into areaction vessel equipped with a nitrogen inlet, a Dean-Starke separatingapparatus, heating means and stirring means. The reaction mixture wasagitated and the temperature was raised to about 197 C. under a nitrogenblanket at atmospheric pressure. At about C., a water-triethylamineazeotropic mixture started to distill off. The azeotropic mixture wascontinuously separated by means of the Dean-Starke apparatus, and thetriethylamine recovered was continuously returned to the reactionvessel. The reaction mixture became almost clear. Then, the temperaturewas allowed to rise to about 230 C. over a one-hour period to remove allthe triethylamine and any excess glycol. The prepolymer product wasallowed to cool under an atmosphere of nitrogen.

EXAMPLE II Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony sec-butoxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury under a nitrogen blanketwhile under agitation for about 2 hours to bring about thepolycondensation of the polyester prepolymer and formation of apolyester resin. The polyethylene terephthalate resin formed had anoriginal intrinsic viscosity of 0.88, a degraded intrinsic viscosity of0.69, and the percentage broken bonds was calculated as 0.132.

EXAMPLE III Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony sec-butoxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury under a nitrogen blanketwhile under agitation for about 2 hours to bring about thepolycondensation of the prepolymer and formation of a polyester resin.After the polycondensation reaction had been completed, 0.02 g. ofdi-n-hexyl sulfone was thoroughly stirred into the polyester resin whilestill molten at atmospheric pressure, after which the resin product wascooled. The resulting polyethylene terephthalate composition had anoriginal intrinsic viscosity of 0.74, a degraded intrinsic viscosity of0.68, and the percentage broken bonds was calculated as 0.050.

EXAMPLE IV Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony sec-butoxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury under a nitrogen blanketwhile under agitation for about 2 hours to bring about thepolycondensation of the prepolymer and formation of a polyester resin.After the polycondensation reaction had been completed, 0.02 g. ofdi-p-tolyl sulfone was thoroughly stirred into the polyester resin whilestill molten at atmospheric pressure, after which the resin product wascooled. The resulting polyethylene terephthalate composition had anoriginal intrinsic viscosity of 0.67, a degraded intrinsic viscosity of0.63, and the percentage broken bonds was calculated as 0.036.

EXAMPLE V Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony sec-butoxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury under a nitrogen blanketwhile under agitation for about 2 hours to bring about thepolycondensation of the prepolymer and formation of a polyester resin.After the polycondensation reaction had been completed, 0.02 g. ofdi-p-hydroxyphenyl sulfone was thoroughly stirred into the polyesterresin while still molten at atmospheric pressure, after which the resinproduct was cooled. The resulting polyethylene terephthalate compositionhad an original intrinsic viscosity of 0.70, a degraded intrinsicviscosity of 0.63, and the percentage broken bonds was calculated as0.068.

EXAMPLE VI Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony sec-butoxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury under a nitrogen blanketwhile under agitation of about 2 hours to bring about thepolycondensation of the prepolymer and formation of a polyester resin.After the polycondensation reaction had been completed, 0.02 g. ofdi-p-ch orophenyl sulfone was thoroughly stirred into the polyesterresin while still molten at atmospheric pressure, after which the resinproduct was cooled. The resulting polyethylene terephthalate compositionhad an original intrinsic viscosity of 0.65, a degraded intrinsicviscosity of 0.62, and the percentage broken bonds was calculated as0.027.

EXAMPLE VII A mixture comprising 600 g. of dimethyl terephthalate, 396ml. of ethylene glycol, and 0.24 g. of lithium hydride was charged intoa reaction vessel equipped with a nitrogen inlet, heating means andstirring means. The reaction mixture was agitated and heated atatmospheric pressure at 198 C. under a nitrogen blanket. The reactionmixture was held at about 198 C. for about two hours, during which timelay-product methyl alcohol was distilled off. Then, the temperature ofthe reaction mixture was allowed to rise to 230 C. over a period ofabout one hour to distill off any remaining by-product methyl alcoholand ethylene glycol and form a polyester prepolymer. The prepolymerproduct was allowed to cool under an atmosphere of nitrogen.

EXAMPLE VIII Fifty grams of the prepolymer product of Example VII wasmixed with 0.02 g. of antimony trioxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury under a nitrogen blanketwhile under agitation for about 3 hours to bring about thepolycondensation of the polyester prepolymer and formation of apolyester resin. The polyester resin formed had an original intrinsicviscosity of 1.13, a degraded intrinsic viscosity of 0.76, and thepercentage broken bonds was calculated as 0.169.

EXAMPLE IX Fifty grams of the prepolymer product of Example VII wasmixed with 0.02 g. of antimony trioxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury under a nitrogen blanketwhile under agitation for about 3 hours to bring about thepolycondensation of the polyester prepolymer and formation of apolyester resin. At the end of the polycondensation reaction, 0.02 g. ofdi-p-tolyl sulfone was thoroughly stirred into the polyester resinproduct and then cooled. The polyester resin formed had an originalintrinsic viscosity of 0.79, a degraded intrinsic viscosity of 0.70, andthe percentage broken bonds was calculated as 0.062.

In the above examples, the original intrinsic viscosity values of thepolyester resin products were obtained by measuring the intrinsicviscosities of the resin compositions as produced.

The degraded intrinsic viscosity values were determined by the followingprocedure: The polyester resin composition was ground and passed througha 10 USS. mesh screen and dried at C. in vacuo for 16 hours, then cooledin a desiccator. Two to three grams of this dried resin was then placedin a test tube which was then inserted into an aluminum block preheatedto 280 C. (i0.5 C.). The block was then sealed and evacuated to 0.1 mm.of mercury. After holding for about 10-15 seconds, the block was filledwith dried, oxygen-free nitrogen gas. This vacuum-nitrogen purge wasthen repeated for a total of three times; the entire process took 5-7minutes. Then, the resin sample was left in the heated block for anadditional two hours under a slow stream of nitrogen. After thistwo-hour period, the resin sample was removed from the block and placedin a desiccator wh Was first GVaCUMe I and then filled with nitrogen.

The intrinsic viscosity of the resin product was then determined andsuch an intrinsic viscosity value is noted in the examples above as thedegraded intrinsic viscosity.

The percentage broken bonds values indicated in the above examples werecalculated by the use of the following equation:

%Broken Bonds: E 5 Ila 9.6

The value of K and a may be found in the literature, such as Conix, A.,Makromol, Chemie 26, p. 226 (1958), wherein K=0.00021 and a=0.82. V, inthe above formula is the degraded or final intrinsic viscosity value andV, is the original or initial intrinsic viscosity value.

All of the intrinsic viscosity determinations of the polyester resinproducts produced in the above examples were determined in a 60%phenol-40% tetrachloroethane solution, Wt./wt., at 30 C., according toconventional laboratory procedure.

The results in the above examples indicate that the present additives,when added to linear polyester resins, act to stabilize or reduce thedegradation eflFects of higher temperatures upon such polyester resins.The change in intrinsic viscosity or the difierence between the originalintrinsic viscosity and the degraded intrinsic viscosity is a directmeasure of the heat stabilizing eifect that the present thermalstabilizers have upon polyester resins and can be readily calculatedfrom the above results.

When the controls above, Examples II and VIII, are compared with theircorresponding examples wherein the same catalyst systems and startingmaterials were used, but with the addition of a thermal stabilizer ofthe present invention, it can readily be seen from the intrinsicviscosity values and the percentage broken bonds values that the presentstabilizers act to limit the amount of degradation that takes place whenpolyester resin products are exposed to elevated temperatures forprolonged periods of time.

The present invention has been illustrated with particular respect tothe stabilization of polyethylene terephthalate. However, the presentthermal stabilizers are also effective in stabilizing any fiber andfilm-forming linear polyesters and copolyesters; for example, thosederived from aromatic dicarboxylic acids, such as isophthalic acid, and4,4-diphenyldicarboxy1ic acid, or ester derivatives thereof, andsuitable diols, such as glycols of the series HO (CH OH, where n is 2 to10.

It will be apparent that various different embodiments can be madepracticing this invention without departing from the spirit and scopethereof, and therefore, it is not intended to be limited, except asindicated in the appended claims We claim:

1. A stabilized polyester composition comprising a linear polyestercontaining a stabilizing amount of a compound selected from thoserepresented by the formula wherein R and R are radicals selected fromthe group consisting of alkyl containing from 1 to 10 carbon atoms,phenyl and chlorine, hydroxyl or lower alkyl (C to C para substitutedphenyl.

2. The composition of claim 1 wherein the polyester is polyethyleneterephthalate.

3. The composition of claim 1 wherein the compound is present in anamount ranging from 0.01% to about 0.5%, by weight, based on the weightof the linear polyester.

4. The composition of claim 1 wherein the compound is di-n-hexylsulfone.

5. The composition of claim 1 wherein the compound is di-p-tolylsulfone.

6. The composition of claim 1 wherein the compound isdi-p-hydroxylphenyl sulfone.

7. The composition of claim 1 wherein the compound is di-p-chlorophenylsulfone.

8. The composition of claim 1 wherein the compound is hexylphenylsulfone.

9. The composition of claim 1 wherein the compound is di-n-octylsulfone.

10. The composition of claim 1 wherein the compound is di-n-ethylsulfone.

References Cited UNITED STATES PATENTS 2,677,617 5/ 1954 Thompson26045.7

2,740,766 4/ 195 6 Stanton et al. 26045.7

3,407,140 10/ 1968 Chiddix et al 260-4595 FOREIGN PATENTS 1,386,36912/1964 France 26045.7

HOSEA E. TAYLOR, .TR., Primary Examiner US. Cl. X.R.

